Communicable Diseases

Communicable diseases are diseases that are transmitted from one person to another person either directly or indirectly. When several people in a particular environment or area acquire a certain abnormality in their health at the same time, that disease outbreak is known to be an epidemic.

On the other hand, a disease is termed an epidemic, if it is found in a lesser extent but continuously in a particular region or area. Pathogens such as viruses, fungi, bacteria and protists cause these diseases.

Most of the diseases which attack the health of man and beast are due to these particular organisms, with thousands of these organisms inhibiting the bodies, working places, resting places and other outdoor locations.

These pathogens may invade the body through the mouth during feeding, through the nostrils, during inhalation, through the anus or through the general organs and some may become parasites on the skin.

A person may develop a sign or symptom of a communicable disease after becoming infected by one of the pathogens.

They may contact these pathogens through:

  • Contact with contaminated fluids such as blood mucus and saliva.
  • Direct contact with an already infected person
  • Consumption of contaminated water of food
  • Receiving a bite from an insect or animal carrying one of the pathogens
  • Inhalations of contaminated air or droplets from an infected person’s cough or sneeze.

Classification of Communicable Diseases

There are many ways and methods of classifying communicable diseases. Some methods used to classify communicable disease are causative agents as the basis.

Others use the length of the incubation period, while some use the media of transmission as the basis.

  • Using causative agents as a basis which involves bacteria diseases, virus diseases, fungi diseases, rickettsiae diseases and protozoan diseases.
  • Using the length of the incubation period as a basis for classification, there are three groups of communicable diseases:
    • Very Short Incubation Period: These are diseases which the incubation period is between 2 to 18 hours. Most common of this group is food poisoning.
    • Short Incubation Period: The diseases in this group range from 2 to 7 days. Pneumonia, infantile gastroenteritis, anthrax, meningitis, diphtheria, influenza and gonorrhea are some examples of this group.
    • Long Incubation Period: This group has incubation periods of 12 to 45 days. Examples are;

Smallpox, whooping cough, typhoid fever (12 days), Chicken pox, Rubella or German measles, mumps, syphilis (17 to 21 days), Rabies (10 to 42 days), poliomyelitis (11 to 14 days), infectious hepatitis (18 to 45 days) but occasionally up to 4 months.

  • Using mode of transmission as a basis of classification, we have;
    • Air-borne Diseases: They are usually respiratory tract diseases. Examples are chickenpox, common cold, influenza, German measles, meningitis, mumps, pneumonia, smallpox, sore throat, tuberculosis and whooping cough.
    • Food and Water-borne Diseases: These diseases spread from human waste such as urine and fecal matter of an infected person. The germs enter the body through the mouth. They are usually gastro-intestinal diseases; cholera, diarrhea, dysentery, food poisoning, meningitis, typhoid fever and infectious hepatitis are some examples.
    • Insect-borne Diseases: These diseases enter the body through a puncture of the skin during the bites from vectors. Examples include malaria fever, typhoid fever, cholera, dysentery, yellow fever, trypanosomiasis (sleeping sickness) and so on.
    • Contact Diseases: Contact diseases are spread by direct contact between the healthy individual and an infected human being or animal or by direct contact with infected materials such as clothing or beddings. In this group are venereal diseases which have constituted a major health problem. Also in the group are trachoma disease of the eye in which the infection is often transmitted by use of towels. Some contact diseases are scabies, ringworm, gonorrhea, syphilis, rabies etc.       

Types and Causes of Communicable Diseases

Communicable disease as earlier stated, is caused by micro-organisms. These organisms are impossible to see or examine with the naked eye, so the function of a microscope is employed. Another term use scientifically for micro-organisms is microbes.

Although a large number of microbes are harmless and some are even beneficial to man, certain number of them causes illness- they are pathogenic. If the body is evaded by pathogens with adverse effect, the victim is said to have an infection.

If the infection is restricted to a relatively small area of the body, it is said to be local but when the whole body is affected, it is said to be generalized or systematic (which are usually spread through the bloodstream).

The major causes of communicable disease include:


  • Bacteria are one cell plants; they comprise the largest group of pathogens.
  • Bacteria are conveniently grouped base on the shape and arrangement of cells as examined under a microscope.
  • Bacilli are rod shaped, straight and slender like sticks. Bacilli diseases include tuberculosis, tetanus and typhoid fever.
  • Cocci bacteria are spherical cells that look like dot. some are arranged in chains- streptococci while others are seen in groups- staphylococci. Diplococci diseases are gonorrhea, meningitis, pneumonia. Streptococci diseases include scarlet fever and staphylococci are responsible for pneumonia and food poisoning.
  • Curved-Rods or bacteria are slightly curved like a comma (,) and they are either vibrio like cholera or spirillum (another form that resembles a corkscrew), an example is syphilis.
  • Bacteria if it overcome the body defensive system, has a fantastic ability to reproduce.


  • Fungi are another group of unicellular/ simple plants that are found growing in dark damped places. Familiar examples of fungi are mushroom, mucor and yeast.
  • Some examples of fungi diseases are ringworm, candidiasis, coccidioidomycosis, blastomycosis, aspergillosis, fungal eye infection, fungal nail infection, mycetoma, mucormycosis, pneumocystis pneumonia and athlete’s foot. Although diseases caused by fungi are few, but some are very dangerous and difficult to cure.


  • Viruses are smallest of all micro-organisms and smallest known living things. They are invisible in the eyes of a light microscope and can be seen only by an electron microscope.
  • Viruses grow only within living tissues.
  • Presently there is no universal classification of viruses.
  • They the cause of quite a large number of diseases, some include; poliomyelitis, hepatitis, smallpox, chicken pox, influenza, mumps, rabies, yellow fever, German measles, common cold, HIV and AIDS.


  • This type of organism was discovered by Dr. Howard T. Ricketts. They probably belong to the plant kingdom and are very similar in appearance with bacteria though so much smaller and unlike bacteria they cannot exist outside a living tissue.
  •  A typical rickettsiae disease is typhoid fever. In most instances, these organisms are transmitted through the bite of insects as lice, ticks and flies.


  • This is the only group of microbes that can be definitely classified as animals because of their mode of nutrition. They are much larger than the bacteria in size and are found in almost anybody of water from moist grass to mud paddles.
  • They are well known to cause some common infections dysentery (caused by amoeba), trypanosomiasis (also known as sleeping sickness caused by flagella), malaria (caused by plasmodium vivas), giardiasis (caused by Giardia), toxoplasmosis (caused by a single-celled parasite known as Toxoplasma gondii), among others.

Prevention of Communicable Diseases

There are specific preventive measures against each of the classes of communicable diseases based on transmission. There are also generally basic preventive measures that could be taken against all communicable diseases. The basic preventive measures of a general nature are;

Personal and community Hygiene

They empower individuals with some degree of natural immunity to most diseases, if the body, clothes, home and surrounding are kept clean. Also sleep, rest, consumption of nutritious food and having adequate physical exercises are included in the personal and community hygiene.

Avoidance of Overcrowded places and situation

Overcrowded places reduce oxygen levels of a place and increases the quantity of carbon dioxide which is injurious to the body.

Isolation of Sufferers

All known patients of communicable diseases should be isolated and quarantined to prevent the spread of such diseases. Touching wild animals should be avoided and animals should generally be kept away from drinking sources of water.

Immunity or Specific Resistance

This is one the ultimate defenses against disease. It is defined as the power of individual to overcome the power of a particular disease or harmful agents.

Vaccination and appropriate Medication

Receiving available vaccinations and taking suitable medications like antimalarial medications when travelling to places of malaria risk. 

Treatment of Communicable Diseases

 Communicable diseases may only cause mild symptoms that disappear without treatment. Others may cause severe symptoms or even potentially threaten life. The treatment for such diseases depends on whether they are bacterial, viral or fungal.

Bacterial infections may require a course of antibiotics medications to help control the infection. The drugs kill off the bacteria and prevent them from replicating.

Chronic Fungal infections require over the counter or antifungal medications prescription. The medications are available in both oral and tropical forms.

In viral infections, vaccines are highly effective for preventing specific viral infections. Vaccines contain a dead or inactive form of a virus; the immune system responds by producing antibodies capable of killing an active form of the virus in the future.

If a person already has a virus, they may require antiviral medication to keep the virus under subjection.


Though communicable diseases are caused by micro-organisms, they require a medium of transmission from carrier to prospective healthy host. The media of spread include air, water, insect and contact.


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